Typescript Discriminated Union Example

AnimalKinds.ts

enum CreatureKind {
  Dog = "Dog",
  Wolf = "Wulf",
  Cat = "Cat",
  Tiger = "Tiger",
}

interface Barker {
  bark: () => string;
}

interface Meower {
  meow: () => string;
}

interface Domesticated {
  play: () => string;
}

interface Wild {
  kill: () => string;
}

type Wolf = Barker & Wild & { kind: CreatureKind.Wolf };
type Dog = Barker & Domesticated & { kind: CreatureKind.Dog };
type Cat = Meower & Domesticated & { kind: CreatureKind.Cat };
type Tiger = Meower & Wild & { kind: CreatureKind.Tiger };

type Canine = Wolf | Dog;
type Feline = Cat | Tiger;

type Creature = Canine | Feline;

const doCreatureStuff = (creature: Creature) => {
  creature.kind === CreatureKind.Dog || creature.kind === CreatureKind.Wolf ?
    alert(creature.bark()) :
    alert(creature.meow());


  creature.kind === CreatureKind.Dog || creature.kind === CreatureKind.Cat ?
    alert(creature.play()) :
    alert(creature.kill());

};

const fido: Canine = {
  kind: CreatureKind.Dog,
  bark: () => "wooof",
  play: () => "with ball"
};

const garfield: Feline = {
  kind: CreatureKind.Cat,
  meow: () => "meow",
  play: () => "with box"
};

const balto: Canine = {
  kind: CreatureKind.Wolf,
  bark: () => "grrrr",
  kill: () => "eat chicken"
};

const shereKhan: Feline = {
  kind: CreatureKind.Tiger,
  meow: () => "rarrr",
  kill: () => "eat human"
};

doCreatureStuff(balto);